The present invention relates to a developer solution for positive-working photoresist compositions. More particularly, the invention relates to a developer solution for positive-working photoresist compositions capable of giving a quite satisfactory patterned photoresist layer free from film residue or scums even in the areas of the finest pattern and greatly improving the resolving power in the reproduction of extremely fine through-holes.
As is known, the photolithographic processing prior to etching and diffusion treatment is an important step in many of the manufacturing processes of semiconductor devices and electronic components such as ICs, photomasks for the manufacture of ICs, printed circuit boards and the like as well as planographic printing plates. In the photolithographic processing, the surface of a substrate is uniformly coated with a so-called resist composition, i.e. a coating composition having sensitivity to actinic rays, e.g., ultraviolet light, X-rays, electron beams and the like, to give a thin layer sensitive to actinic rays which is irradiated pattern-wise with the actinic rays followed by development with a developer solution to form a patterned resist layer which serves to selectively protect the substrate surface from etching or diffusion of dopants.
When the above mentioned resist composition has sensitivity to ultraviolet light, it is usually called a photoresist composition which may be either positive-working or negative-working. A photoresist composition of the positive-working type has such a photosensitivity that the solubility of the composition in the developer solution is increased by exposure to light so that the patterned photoresist layer is formed on the areas unexposed to the ultraviolet where the composition is left undissolved. A photoresist composition of the negative-working type exhibits behavior of a sensitivity and solubility which is reverse to that of the positive-working ones. Typical positive-working photoresist compositions include those composed of an alkali-soluble novolac resin as a film-forming component and a naphthoquinone diazide compound as a photosensitizing component. While such a positive-working photoresist composition containing a naphthoquinone diazide compound can be developed by using an aqueous alkaline solution, the alkaline developer solution should be free from any metallic ions because contamination of semiconductor materials with metallic ions is very detrimental to the performance of the devices prepared from the semiconductor material. In this regard, the most widely used metal ion-free developer solution for positive-working photoresist compositions is an aqueous solution of, for example, tetramethylammonium hydroxide disclosed in IBM Technical Disclosure Bulletin, volume 3, No. 7, page 2009 (1970) or choline disclosed in U.S. Pat. No. 4,239,661.
Along with the recent progress in the technology of semiconductor devices with a requirement for finer and finer high-fidelity patterning of a line width of 1 .mu.m or even finer to comply with the trend of increased density of integration in semiconductor devices, the photolithographic process of patterning using a positive-working photoresist composition also envisages a difficult problem. When patterning is desired of an extremely fine contact hole in a fine pattern, namely, it is usual that the above mentioned metal ion-free alkaline developer solution is admixed with a surface active agent with an object to increase the wettability of the substrate surface with the aqueous developer solution. One of the problems in the addition of a surface active agent to the developer solution is that film residua and scums sometimes occur on the exposed areas where the photoresist layer should be dissolved away as completely and cleanly as possible. Such an undesirable phenomenon cannot be completely avoided not to give a clean patterned photoresist layer even by an over-exposure or over-development. Although the film residua and scums can be removed by gently treating the surface with oxygen plasma or sputtering, no complete solution of the problem can be obtained thereby because such a treatment must be performed under well controlled troublesome conditions and is not quite efficient in respect of smooth removal of the scums or gives no uniform effect of treatment in very finely patterned areas having contact holes of about 1 .mu.m or smaller diameter.
When subsequent processing of the substrate surface, such as dry etching, is performed with such film residua and scums removed only incompletely, disadvantages are naturally caused that the uniformity of etching is poor or accuracy of the dimensions or patterned form of the etched areas may be low.